Dietary nucleotides in the diets of on-growing grass carp (Ctenopharyngodon idella) suppress Aeromonas hydrophila induced intestinal inflammation and enhance intestinal disease-resistance via NF-κB and TOR signaling

Abstract

The beneficial influences of nucleotides on fish intestinal immune responses and the mechanisms underlying the regulation of on-growing grass carp (Ctenopharyngodon idella) were evaluated using A. hydrophila induced intestinal inflammation model in vivo. Sixty days growth trial was carried out and fish were fed with mixed nucleotides diets: 0, 200.0, 400.0, 600.0, 800.0 and 1000.0 mg/kg diet. At the end of growth trial, grass carp were faced with infection trials with the challenge of A. hydrophila over a period of 14 days. Studies demonstrated that nucleotides supplementation had a powerful effect on inhibition of enteritis morbidity and inflammation caused by A. hydrophila in fish intestine. Dietary nucleotides elevated the production of intestinal acid phosphatase, lysozyme (LZ) activities, complements, immunoglobulin M and increased intestinal antimicrobial peptides (hepcidin, β-defensin-1, liver expressed antimicrobial peptide 2A and 2B) and mucin2 [only in distal intestine (DI)] gene expression. Nucleotides inhibited intestinal pro-inflammatory cytokines mRNA levels [interferon γ2 (IFN-γ2), tumor necrosis factor α (TNF-α), IL-6, IL-15, IL-17D, IL-12p35 and IL-12p40], which were correlated with nuclear factor kappa B (NF-κB) signaling [IκB kinase (IKK-β and IKK-γ)/inhibitor of (κBα) (IκBα)/NF-kB (p65 and c-Rel)]. Nucleotides increased intestinal anti-inflammatory cytokines [IL-11, transforming growth factor β1 (TGF-β1), IL-4/13A and IL-4/13B] gene expression partly associated with target of rapamycin (TOR) signaling [TOR/ribosomal protein S6 kinases 1 (S6K1) and eIF4E-binding proteins (4E-BP1)]. In summary, dietary nucleotides could enhance intestinal immune responses of fish via the inhibition of NF-κB and the promotion of TOR signaling. Furthermore, based on the parameters of enteritis morbidity and LZ activity in proximal intestine (PI), middle intestine (MI) and DI, optimal nucleotides supplementation levels for on-growing grass carp were estimated to be 580.35, 622.53, 613.21 and 617.98 mg/kg diet, respectively.